Interaction

General Interaction Issues

Use: Use a simple point-and-click interface with large buttons.
Do not use: dragging, double-clicks, scroll bars, dropdown menus, multiple windows, or other elements that can confuse the common user and interfere with usability and efficiency.

Cursor: Turn the cursor off - user will focus on the entire screen instead of the arrow and their thinking and action will be direct instead of indirect.

Textual and Numerical Data Entry with Button Keys

Key arrangement for text entry

Alphabetic keyboards on the screen may have a different order that usual typewriter keyboards. Make the keyboard layout switchable or even customizable. Reason:

Users may not be proficient typist and are not familiar to the typewriter keyboard layout. A different ordering, e.g. alphabetic, may be better suited for them. Use the standard layout only when people are used to it and find the keys faster with this layout.

Minimize text entry

The conventional keyboard layout is not optimal for 10-finger typing. Alternative layouts have been proposed, but are not widely used. Both, the alternative and the standard layout are used for multiple-finger entry. This is not the case with touchscreens. Here people use just one finger, which slows down text entry considerably. Therefore, keep text entry to a minimum or better even avoid it totally on touchscreens.

Key arrangement for number entry

Conventionally, a 3*3 layout is used for number entry. However, there are two layouts used:

the telephone layout (1 upper left)
the keypad layout (1 lower left)

Use the telephone layout for untrained users, because they find the numbers easier with this sorting order, and they may be used to telephones.

Use the keypad layout only for people who are used to it, who prefer it, and who might get into conflicts with the telephone layout. Note that the keypad layout on keyboards is for multiple-finger entry. On touchscreens, however, numbers are entered with one finger only and sequentially.

Minimize number entry

Number entry is very fast on numerical keypads where several fingers of one hand may be used. On touchscreens only one finger may be used which slows down number entry. Therefore do not use touchscreens for heavy use with number entry.

Selections

Selection is an important form of interaction on touchscreens. Users may select:

Actions (via pushbuttons or menus)
Options
Data from a fixed or variable set

Selection on touchscreens is usually done with fingers. Therefore, for selection controls the same size requirements exists as do exist for pushbuttons.

As textual or numerical data input through a virtual keyboard is not well suited to touchscreens, data entry by selection is one important input method for touchscreens.

Selections may also be done indirectly:

The selection can be moved through the items via pushbuttons, e.g. directional pushbuttons
The selection may stay fixed; the items are moved to the selection area through pushbuttons, e.g. directional pushbuttons

Scrolling

With touchscreens, it is easier to scroll by pointing than by dragging. Therefore, we propose:

Do not use conventional scroll bars, even if they are enlarged, but to use simple pushbuttons instead
In addition, the scroll buttons may may a repeat function. The repeat function should start after a predetermined delay (not too long), and then repeat the scrolling while the screen is touched
Scroll buttons should follow the usual guidelines for buttons. Better make them larger than too small

Do not use scrolling for the screen itself, but only for data display, i.e. for fixed areas on the screen. At best, do not use any scrolling at all.

In some cases you can replace scrolling through controls that display only a part of the items or functionality on the screen and that allow for easy switching between the views by pointing to buttons. A tabstrip is such a screen element.

Gestures

Simple gestures, that are easy to remember, can be used on stylus-operated touchscreens for often-used functions. Gestures are simple "drawings" like letters or symbols. Here are a few examples:

Deleting items by striking them through or crossing them out (the Apple Newton used a "W" for this operation.
Marking items by adding a cross ("X") or "Ã".
Identifying a user by his or her signature (handwriting).

Gestures are not well suited to finger-operated touchscreens, as the use drag operations with fingers are not recommended in the literature.

Feedback

Buttons should give some sort of feedback as to their state (on/off, active/inactive, activated (transient), etc.).

Immediate feedback: Critical to reassure the user that their touch registered.
Visual feedback (highlighting, 3 D-effect): In response to button presses.
Auditory feedback (click, ...): Is sometimes also appropriate.
Screen changes: Clear the display clears immediately and displays an hourglass while loading the next screen.
Digitized speech: Can walk users through your application.

Note: Nowadays, feedback is often given, while the mouse pointer is over the pushbutton. However, this behavior cannot be implemented on touchscreens!

Error Robustness

Confirmation after selection: Use it when the consequences are destructive or difficult to undo, minimize inadvertent button selections.

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